1. Field of the Invention
The present invention relates to the art of axle/suspension systems for vehicles. More particularly, the invention relates to the art of sensor systems for steerable and liftable axle/suspension systems of heavy-duty vehicles, such as tractor-trailers or semi-trailers, and straight trucks. Still more particularly, the invention relates to a sensor system that triggers lifting of a certain one of the axle/suspension systems and associated wheels of a heavy-duty vehicle during predetermined maneuvering situations.
2. Background Art
Heavy-duty vehicles such as tractor-trailers and straight trucks typically include multiple axles that are longitudinally spaced along the vehicle to create ride stability. At times, it is necessary to lift at least one of the axles, including the suspension assemblies and wheels and tires that are associated with the axle. For example, it may be necessary to lift an axle when the vehicle is performing an extremely tight turning maneuver, which frequently occurs on private property at a loading facility. The axle that is lifted is commonly referred to as the lift axle, and typically is a forward axle or a rearward axle of a plurality of longitudinally-spaced axles that are suspended from the vehicle. For the purpose of convenience, reference herein will be made to a lift axle that is a forward axle. The non-liftable axles in the group that are rearward of the lift axle are known in the art as primary axles.
The actual lifting of the lift axle is performed by the transversely-spaced suspension assemblies that are associated with the lift axle, with such lift axle/suspension systems being well-known in the art. The lift axle/suspension system typically is operated by a control system that is in turn actuated by a switch, commonly referred to as a lift switch, which is manually triggered by the operator of the vehicle. Lift switches traditionally have been installed in the cab of the vehicle for proximity to the operator. This prevents an operator from having to exit the cab, which can be particularly inconvenient in circumstances such as inclement weather.
Recently, laws have been enacted in Canada which direct that axles that had previously been lifted for maneuverability must now instead be steerable axles. That is, the axle may not be lifted for maneuverability when moving in a forward direction, but must instead remain on the ground and steer to attain maneuverability. Such steerable axles are well-known in the art, and it is also well-known in the art that steerable axles are capable of being lifted. Hence, for the purpose of simplicity, reference herein will be made to steerable axles with the understanding that steerable axles include lift axles.
The new laws still allow a steerable axle to be lifted when the vehicle is moving in reverse, since certain widely-used systems do not operate to steer the steerable axle when the vehicle is moving in a reverse direction. To ensure that the steerable axle is not lifted while vehicle is moving over-the-road in a forward direction or making a forward turn maneuver, however, the recently enacted laws do not allow a lift switch in the tractor cab.
These new laws have generated a great deal of concern for tractor-trailer operators, since problems can occur when a vehicle having a steerable axle attempts an extremely sharp turn, which often happens when the vehicle is being maneuvered to align with a loading dock. Space limitations imposed by the arrangement of the suspension beams and trailer frame rails typically do not allow the wheels that are mounted on a steerable axle to be turned more than about twenty to thirty degrees from the longitudinally-extending centerline of the vehicle. It is to be noted that the angle of the wheels that is required to make a turn, relative to this longitudinally-extending centerline, is known as the wheel-cut angle. Thus, in typical heavy-duty vehicle arrangements, when the wheel-cut angle is greater than about twenty to thirty degrees, the wheels on the steerable axle cannot turn to the degree that is required, remaining at an angle of only about twenty to thirty degrees.
The resulting adverse condition caused by the inability of the wheels of the steerable axle to execute a wheel-cut angle of more than twenty to thirty degrees is tire scrub, also known as drag. In some tight turning maneuvers, the angle between the tractor and the trailer often approaches ninety degrees. In such a maneuver, when the wheels and tires of the steerable axle are not lifted, they are effectively prevented from rolling since they can turn to an angle of only about twenty to thirty degrees, and are thus dragged in the direction of the turn. This undesirable situation causes scrubbing, or excessive wear of the tires, and results in the need to more frequently replace the tires of the steerable axle, thereby creating increased vehicle operation costs.
In addition, the steerable axle typically is located at about the center of the trailer in the fore-aft direction and usually uses a single tire on each of the wheels at the axle ends. Such single tires each have a large area of contact with the ground. In a tight turning maneuver, the central positioning of the steerable axle combines with the large area of contact of the tires and the severe angle between the tractor and the trailer, thereby causing the wheels of the steerable axle to act as a pivot point. The tires on the wheels of the primary axles are roughly at right angles to the directional forces acting on the trailer, forcing these tires sideways and scrubbing them. The scrubbing of the tires on the primary axles further increases the problems of more frequent tire replacement and decreased vehicle maneuverability.
One solution to the scrubbing problem would be to increase the wheel-cut angle for the wheels of the steerable lift axle. However, as mentioned above, the arrangement of the suspension beams and trailer frame rails imposes space limitations that, in turn, limits the wheel-cut angle to about twenty to thirty degrees. Thus, a solution involving an increased wheel-cut angle would necessarily involve relocation of the suspension beams and frame rails. Due to the performance requirements that are associated with a heavy-duty vehicle, however, such as roll stability and load capacity, structural requirements are imposed that do not allow the frame rails and suspension beams to be substantially relocated. As a result, structural changes cannot readily be accomplished that would allow the wheel-cut angle to significantly exceed about twenty to thirty degrees, let alone a greater angle approaching about ninety degrees, as is desired for tight turning maneuvers.
In an attempt to reduce these scrubbing problems, the new laws that mandate the use of a steerable axle permit the lifting of the steerable axle when a manual lift switch is located on the trailer near the steerable axle, rather than inside the tractor cab. This would allow a driver to execute a drag-turn maneuver of the type usually performed at a loading facility, which typically is located on private property, without scrubbing tires. To use such a switch, however, the driver must exit the cab, engage the switch to lift the steerable axle, re-enter the cab, complete the tight maneuver, exit the cab again, re-engage the switch to lower the axle, re-enter the cab, and finally continue on his way. Because weather conditions often may be harsh, particularly during winter in countries such as Canada, the exercise of the driver repeatedly exiting the cab to engage a manual switch to lift and lower the steerable lift axle is very inconvenient and potentially dangerous.
Thus, a need exists in the art for an apparatus that overcomes the problems of the prior art by allowing a steerable axle to be lifted during tight maneuvering of a vehicle without the need for a driver to exit the cab of the vehicle, yet without the use of a manual lift switch located in the tractor cab. The present invention provides such an apparatus, which automatically causes a steerable axle to be lifted in tight turning maneuvers.